With all the rain we had earlier in the summer, pre-emergence products may not have lasted long enough and now you can find annual crabgrass or goose grass in the lawn. If the crabgrass is not too big, pulling it up before it sets seed is a start. Crabgrass that has increased in size has smothered the lawn grass below, leaving an open spot 3-5 inches in diameter. Top-dress that spot and reseed to establish the seed before winter. Leaving it open is an invitation for more crabgrass next spring or other annual weeds to invade that spot.
Broadleaf perennial weeds like dandelion and plantains have sprouted from seed and are young plants ready to overwinter and show up in a bigger way next spring. Broadleaf weed control in the late summer and early fall should leave you with a lawn free of dandelions next spring.
If there weeds are consistently returning or persisting in parts of the lawn, consider actions that favor the growth of the grass and not the weeds. Weeds like knotweed, prostrate spurge and purslane can grow in compacted soils while grass cannot. Breaking up that compaction will favor the grass and make it more competitive against the weeds. A thicker, fuller lawn shades the soil, preventing sunlight from reaching the ground, something weed seeds need to germinate. Consider raising the mower deck up just one notch to leave the lawn a bit longer to create more shade.
If you feed your lawn with traditional products and you only fertilize once a year, fall is the best time. The grass roots will continue to grow well into the late fall and store that energy for next spring. Homeowners wanting to improve the soil using organic matter can apply that as a top-dressing. As the organic matter breaks down further, it will release nutrition to the grass plants. Top-dressing with organic matter will also help manage the thatch layer too.
This time of year also brings along the possibility of grubs in the lawn. Fortunately for us, the beetles that lay the eggs in lawn have been far fewer than in the past. Japanese beetles can feed on a wide range of plants as an adult, but will need to lay their eggs in the lawn. Treatments are warranted if there are more than 12 grubs per square foot. The lawn will pull up and down like it was recently laid sod. Using a garden spade to assist in the removal of the grass, grubs will be bright white in color with a tan or brown head and will curl up into a "C" when disturbed and very easy to spot. There are other beetles that lay eggs in the lawn, but the Japanese beetles have taken the lead over our more native insects.